The proposed research will investigate the role of Beta-carotene as a lung cancer preventive agent. A high risk cohort of men occupationally exposed to asbestos and a selected group of hospital patients with abnormal sputum cytopathology will be used for a randomized clinical trial of Beta-carotene versus placebo. Bronchial epithelial changes, evaluated by repeated sputum cytology, will be used as the measure of response to the chemopreventive agent. Serum levels of Beta-carotene will be studied with respect to the degree of sputum metaplasia or dysplasia found at initial examination and with respect to bronchial epithelial changes throughout the clinical trial.